Water heaters are used in homes, businesses and in just about any establishment having the need for heated water. A conventional water heater typically has at least one heating element or “heater,” such as a gas-fired burner and/or electric heating element. Each water heater also typically has at least one thermostat or controller for controlling the heater. The controller typically receives signals related to the temperature of the water within the water heater tank, often from a temperature sensor that is thermally engaged with the water in the water heater tank.
In some instances, a water heater may operate in accordance with a first temperature set point and a second temperature set point. The difference between the first and second temperature set point may be referred to as the temperature differential of the water heater. When temperature signals from the temperature sensor indicate that the water temperature is below the first set point, for example when the water temperature is below about 120° F., the controller may turn on the heater and the water within the water heater tank begins to heat. After some time, the water temperature within the water heater tank will increase to the second set point, which, for example may be about 140° F. At this point, the controller may cause the heater to reduce its heat output or, alternatively, causes the heater to turn off. This heat cycle begins again when the water temperature within the water heater tank cools down below the first set point.
For a gas fired water heater, a temperature sensor, a gas valve and a controller are often mounted relative to the water heater tank. The controller typically receives a temperature signal from the temperature sensor. The temperature sensor often protrudes into and is thermally coupled to the water in the water heater tank. The controller typically is programmed to control the gas valve such that the temperature of the water in the water heater tank remains between the first and second temperature set points, as described above. For an electric water heater, a temperature sensor, a power delivery unit and a controller may be mounted to the water heater tank. In this case, the controller may control the power delivery unit such that the temperature of the water in the water heater tank is kept between the first and second temperature set points.
Typically, a water heater is sized to service an expected peak hot water demand for a particular application. As such, for applications with higher peak hot water demands, the size of the water heater may need to become fairly large. Larger water heaters, however, can be less energy efficient than smaller water heaters. What would be desirable, therefore, is a water heater system that can satisfy fairly large hot water demands, but in a more energy efficient manner.